There is a wide variety of coin-operated devices that utilize some mechanism for identifying valid coins; vending machines, slot machines, and arcade video machines just to name a few. There are also many ways to circumvent the proper operation of these machines. For example, slugs, foreign coins, tilting the device, and the retrievable coin-on-a-string routine are traditional gimmicks that have been employed over the years to cheat various coin-operated devices. Accordingly, a variety of coin testing devices have been designed in an attempt to defeat these and other gimmicks.
Indeed, over the years, a number of coin identifier devices have been designed. Simple identifiers have included detecting the size and/or the weight of the inserted coin, but are often susceptible to one or more of the commonly known cheating devices. For example, a coin identifying mechanism that operates by detecting coin size is susceptible to slugs or foreign coins having a similar size. Likewise, coin identifying mechanisms that operate by detecting the weight of an inserted coin are also susceptible to both slugs and foreign coins.
Coin detector and identifying systems that utilize magnetic fields are known to provide excellent detection and matching capability, and are not easily defeated by the traditional cheating gimmicks. An example of a magnetic field-type coin detector is disclosed in U.S. Pat. Nos. 4,437,558 and 4,469,213, both assigned to the assignee of the present invention and incorporated herein by reference. The coin detection device disclosed in the '213 patent utilizes three aligned electric coils. The two outer coils are electrically connected in series with an oscillator circuit. The oscillating current within these coils establishes a magnetic field about each coil. Since the current through the series connected coils is the same, the magnetic fields established about each of these two coils is identical. The center coil is passively connected to an amplifier, the output of which is an amplified indication of the magnetic field established within the center coil. The outer coils are aligned with the center coil in opposing relation, so that the electric fields generated by the two outer coils generally cancel in the region of the center coil, leaving a net electric field of zero within the inner coil. Accordingly, no voltage is induced at the terminals of the center winding, indicating a matched condition about the center coil.
A sample coin (of any type) is physically disposed between the center coil and one of the two outer coils, thereby interrupting the electro-magnetic field established therebetween. More specifically, the coin (due to its physical characteristics) will attenuate the magnetic field in the region of the coin. As a result, the opposing electric fields from the two outer coils is no longer centrally balanced, and a net electric field exists within the center coil. Thus, a voltage is induced across the terminals of the center winding, driving the amplifier to saturate.
Coins inserted by a user into the coin-operated device are routed through a chute so as to pass through the space physically separating the center coil and the opposing outer coil. When the sample coin and test coin differ both in size and in structure (e.g., material composition) a net magnetic field remains in the centrally disposed coil. When, however, the coins identically match, the net magnetic field within the central coil is substantially zeroed out. This condition signals a valid and identified coin which may then be accepted by the device.
While the coin detector and identifier circuit of the '213 patent provides an effective means of detecting and identifying coins, it is known to be susceptible to electromagnetic interference (EMI). Indeed, in recent years the proliferation of transmitting devices such as cellular telephones has been tremendous. As a result, occasional failures occur in the coin detector and identifier described in the '213 patent. To illustrate this failure, consider a test coin inserted in the machine that precisely matches the sample coin. In the absence of electromagnetic interference, the net magnetic field within the center coil has a net magnitude of zero (or substantial zero). If, however, extraneous electromagnetic interference is present, a net magnetic field within the center coil will be present. If the magnitude of the EMI is sufficiently great, the coin detector and identifier may improperly reject an otherwise valid coin (false failure). Accordingly, improvements are sought to be made to the coin detector circuitry of the '213 patent.
Another area in which the mechanism of the '213 patent is sought to be further improved relates to device circumvention achieved by either tilting the coin operated device or defeating its proper operation by use of the coin-on-a-string gimmick. An otherwise valid test coin may be inserted in the machine but attached to a string in a manner that, once properly identified by the detection circuitry, may be jerked back and removed from the machine. Alternatively, if the coin-operated device is small enough it may be shaken or tilted. This may lead to improper multiple counts of a single coin. That is, once a test coin has been sensed and identified by the detector circuitry, improperly tilting the coin-operated device may cause the coin to back up and pass through the sensing circuitry again, affectively double-counting the single coin and, thus, circumventing the proper operation of the coin-operated device. Accordingly, it can be appreciated that an improved coin detector and identifying machine is desired. More specifically, it is desired to provide a coin detection and identifying machine that offers improved resistance to the traditional gimmicks, but is also desensitized to high levels of electromagnetic interference.